Pine white butterflies flit to new homes in Washington desert

Sep 7, 2011

RICHLAND, Wash. – It's been 30 years since the last outbreak, but now white butterflies are flitting between pine trees across areas of eastern Oregon and Washington.

From Bend to Spokane, pine trees have become home to large populations of pine white butterflies this summer. These occurrences have happened decades apart, notably in the 1890s and 1920s, and usually last about two to three years.

Washington State University entomology professor Richard Zack says no one’s really sure what causes the population explosion.

“There will be some years when you can’t find one of these butterflies,” Zack says. “And other years, like we’re finding now, where it just seems like they’re flying all over the place.”

Zack says many times – in large occurrences like these – pine white butterflies are blown from place to place.

Planted trees help spread

However, unlike previously, the butterflies have landed in the Tri-Cities, a high desert climate in southeastern Washington. All thanks to urban development.

Pines are among the 5,000 trees the City of Richland has planted overtime throughout its parks, with more to come. And that doesn’t include pine trees planted in people’s yards. In general, no trees are native to the naturally barren area. This change in landscape has provided a home for pine white butterflies.

“I would think in those 1920 outbreaks,” Zack says, “you probably would have had a hard time finding one of those butterflies anywhere in what would have been the Tri-Cities at that time because there would not have been a pine tree.”

Zack says the new-to-the-area butterflies are now here to stay.

The butterflies could damage some trees, particularly ponderosa pines. But Zack says damage varies from tree to tree, year to year. It will be apparent as caterpillars feed on needles next spring. But, he says, with pine trees in relatively healthy condition throughout the region, there won’t be many problems.